Consider a color layer to be opaque if its alpha is 1.0

Remove layers occluded by an opaque color layer from going
into composition.

Bug: 136561771

Test: atest SurfaceFlinger_test
Test: Add a full screen color layer with an alpha of 1 and check layers
      behind the layer are consided occluded, and the layers are not
      composed.

Change-Id: Iede63ae4d3e378e650c0b0e7364d0c8d128e3105